The present invention relates to a determination of polarization dependent properties of an optical device under test—DUT.
Determining polarization dependent parameters like polarization dependent loss (PDL) and polarization dependent group delay PDGD, covering both the Differential Group Delay DGD and the Polarization Mode Dispersion PMD, is of high importance for advanced optical communication systems.
Today's solutions for determining a polarization behavior of a device under test, e.g. polarization dependent loss parameters, comprise scrambling methods, i.e. applying a random variation of polarization states and comparing maximum with minimum loss determined from the signal responses, and analytic methods like the so-called Mueller method. Within the Mueller method, a device under test, e.g. a transmission fiber, is stimulated with 4 defined polarization states, and the optical power of the corresponding input signals applied to the DUT and the output signals received from the DUT are measured and analyzed together. This method is described in more details in ‘Fiber Optic Test and Measurement’ by Dennis Derickson, ISBN 0-13-534330-5, 1998, pages 354-358.
U.S. Pat. No. 6,671,038 discloses a method of measuring polarization dependent parameters of a DUT in dependence of the wavelength, wherein a polarization translator is connected between a tunable light source and the DUT. When sweeping the wavelength of the light source, the polarization translator provides to the DUT a signal wherein the polarization is periodically changing over the wavelength. In each wavelength range, a plurality of different polarization states are provided to the DUT, thus allowing a determination of polarization depended parameters by detecting the corresponding power values returning from the DUT.